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Complimentary use of dating and hydrochemical tools to assess mixing processes involving centenarian groundwater in a geologically complex alpine karst aquifer
  • +2
  • J.M. Gil-Marquez,
  • Beatriz De la Torre,
  • Matías Mudarra,
  • Jürgen Sültenfuß,
  • Bartolomé Andreo Navarro
J.M. Gil-Marquez
Universidad de Málaga
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Beatriz De la Torre
Universidad de Málaga
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Matías Mudarra
Universidad de Málaga
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Jürgen Sültenfuß
University of Bremen
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Bartolomé Andreo Navarro
Universidad de Málaga
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Peer review status:ACCEPTED

22 Mar 2020Submitted to Hydrological Processes
24 Mar 2020Submission Checks Completed
24 Mar 2020Assigned to Editor
24 Mar 2020Reviewer(s) Assigned
10 May 2020Review(s) Completed, Editorial Evaluation Pending
10 May 2020Editorial Decision: Revise Minor
10 Jun 20201st Revision Received
10 Jun 2020Submission Checks Completed
10 Jun 2020Assigned to Editor
10 Jun 2020Reviewer(s) Assigned
10 Jun 2020Review(s) Completed, Editorial Evaluation Pending
10 Jun 2020Editorial Decision: Accept

Abstract

Environmental dating tracers (3H, 3He, 4He, CFC-12, CFC-11, SF6) and the natural response of spring (hydrochemistry, water temperature, and hydrodynamics) were jointly used to asses mixing processes and to characterize groundwater flow in a relatively small carbonate aquifer with complex geology in South Spain. Results evidence a marked karst behavior of some temporary outlets, while some perennial springs show buffer and delayed responses to recharge events. There is also a general geochemical evolution pattern, from higher to lower altitudes, in which mineralization and the relation Mg/Ca rises, evidencing longer water-rock interaction. The large SF6 concentrations in groundwater suggest terrigenic production, while CFC-11 values are affected by sorption or degradation. The groundwater age in the perennial springs deduced from CFC-12 and 3H/3He point out to mean residence times of several decades, although the difference between both methods and the large amount of radiogenic 4He in the samples indicates a contribution of old groundwater (free of 3H and CFC-12). Lumped Parameter Models and Shape-Free Models were created based on 3H, tritiogenic 3He, CFC-12, and radiogenic 4He data in order to interpret the age distribution of the samples. The resulting groundwater-age distributions evidence the existence of two mixing components, with an old fraction ranging between 160 and 220 years. Some dating parameters derived from the mixing models and their correlation to physicochemical parameters permits to explain the hydrogeochemical processes occurring within the system. All these results prove that large time residence times are possible in small alpine systems with a clear karst behavior when the geological setting is complex, and they highlight the importance of applying different approaches, including groundwater dating techniques, to completely understand the groundwater flow regime within this type of media.